A cryotube is a cylindrical plastic container classically composed of two elemental pieces: the tube and the plug. The tightness of the assembly of these two pieces (generally by screwing) permits preservation of specimens inside the cryotube at variable temperatures that can drop according to the models down to −196° C. (liquid nitrogen), whence the term “cryo” tube.
Tubes that can contain specimens to be frozen under liquid nitrogen are known.